The present teachings improve on Buffer Status Report (BSR) reporting and triggers in Long Term Evolution (LTE) or satellite communication systems that borrow from the LTE specification and Medium Access Control (MAC) Specification with respect to backlog reporting. In the prior art, LTE and satellite communication systems that use BSR reporting do not get an updated backlog information adequately based on new packet arrival at a User Terminal (UT) without excessive overhead. The present teachings disclose improved reporting without excessive overhead and are compatible (robust) with an eNodeB configuration of other timer control LTE baseline BSR reporting.
A description of the prior art's LTE backlog and BSR reporting is provided in section 5.4.5 of 3GPP 36.321 Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC); Protocol specification (Release 10) (hereinafter “[1]”) included herein in its entirety by reference. In the prior art, there are three different ways the BSR is triggered. The different triggers are as follows:                Regular BSR occurs when data arrives at an empty buffer;        retxBSR-Timer expires and there is data pending at the UT, configurable with a minimum of 320 ms per “3GPP 36.331 Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification (Release 10)”.        periodicBSR-Timer is called a referred to a “Periodic BSR”        
Also per section 5.4.4 of [1], only a Regular BSR can trigger a Scheduling Request (SR) if configured for a particular logical channel. In other words, an SR is sent only when data arrives at an empty buffer or a retxBSR-Timer expires while no uplink allocation is given for the particular logical channel. An exemplary BSR is described in section 6.1.3.1 of [1].
In general, satellite communication systems have longer link delays than what is experienced in LTE. The shortcoming of the above triggers, especially if the BSR is used in a satellite communication systems, is that an eNodeB or satellite gateway is not aware of the new packet arrival to a non-empty buffer unless a periodicBSR-Timer happens to expire at that time.
FIG. 1 illustrates exemplary BSR triggers for a prior art system.
A prior art BSR trigger system 100 includes a User Terminal (UT) 102 and a bandwidth allocator 104. The bandwidth allocator may be included in a satellite gateway or eNodeB. The UT 102 may be in an empty buffer state 110. At state 112, the UT 102 reports a buffer status or demand of N1 bytes, for example, 2000 bytes, at time t0. Per FIG. 1, at time t0+20 ms (state 114), the UT 102 gets a buffer status or demand of N2 bytes, for example, 4000 bytes to be transmitted from an upper layer. In the prior art, the new packet arrival of N2 bytes does not trigger a transmission of a new BSR as the new packet of N2 bytes did not arrive at an empty queue.
At time t0+40 ms (state 116), the UT 102 gets an uplink allocation of four (4) packets of 500 bytes each to satisfy the N1 (2000 bytes) request of the buffer from the bandwidth allocator 104. After granting the uplink allocation, the bandwidth allocator 104 (for example, eNodeB or gateway) assumes that it has fully satisfied a backlog of the UT 102 or the backlog associated with a logical channel group (LCG) (per LTE terminology). This first operation satisfies N1.
The assumption by the bandwidth allocator 104 is incorrect, as the UT one or two now has 4000 bytes of backlog (per state 114) sitting in the queue, which backlog did not trigger an SR or send a BSR to request additional uplink allocation. The lowest allowed duration for the retxBSR-Timer in the UT 102 is 320 ms per LTE. Furthermore, the UT 102 can only request an SR when the retxBSR-Timer expires at time t0+320 ms (state 118). After the SR (state 120), the UT 102 will get an uplink allocation (state 122) in which it will inform the bandwidth allocator 104 of the backlog if the backlog of the UT 102 has not been fully satisfied. Based on the BSR, the bandwidth allocator 104 would allocate the appropriate uplink resources (state 124). As such, in the best case, the appropriate uplink allocation to satisfy N2 is only granted after 320 ms (retxBSR-Timer)−20 ms (arrival of N2)+2*Round Trip Time has elapsed from the time the data (N2) arrived at the UT 102. This second operation gets an uplink allocation for N2.
Per the third trigger noted above, the UT 102 would have sent BSR if periodicBSR-Timer was configured to be less than 40 ms. The reporting is based on the configuration of a periodicBSR-Timer by the bandwidth allocator 104. Setting the timer to a low value results in too frequent reporting and associated overhead. Furthermore, the updating of the bandwidth allocator 104 by the UT 102 and a scheduler for a demand for 4000 bytes is dependent on a timing of the arrival of packets from an upper network layer (not shown) and the expiry of the periodicBSR-Timer.